METRIC ! 52

[ceesjan]

Don't you think it's time for engineers all over the world to use the same system?? Ofcourse this must be the metric system!

c-j

 

[TheBlacksmith]

In many cases, I believe the system should be governed by what the suppliers have available and what the "mechanics" are used to. In the US, there are a lot of things such as bolts, rods, beams etc. that are still manufactured in English units. Admittedly, the US school system has done a dismal job of teaching metrics - my opinions here are no surprise. I think it is the duty of the Engineers to take the element of human failure/mistake out of the design to the maximum extent practical. Why should decide that a 1/4-20, grade 5 bolt will substitute for a 5 mm 8.8 bolt, the degreed engineer, the purchasing agent or the guy assembling the component? I have happily worked in several systems, according to the majority around me at the time to avoid confusion. Look at pressure for one example; inches of mercury, centimeters of mercury, inches of water, feet of water, bars, pascals, atmospheres, pounds per square inch - depends on the component and country you're dealing with.



Blacksmith

 

[JLW]

It would be nice, but until the U.S. makes the switch to metric for get it.
I’m sure also that many of us are growing accustom to the imperial system (like I have) because the majority of companies customer bases are in the states.

 

[brad]

Depending on the industry, in some cases the US already is metric. Nearly all engineering for American automobiles is done in metric units. This has been the case for a decade. There are still vestiges of the English system (generally found in the test laboratories and plants, which are older and consist of older-generation workers). However, parts are designed, analyzed, and spec'ed in metric.
Everyone other than engineers and scientists are still kicking and screaming . . .
Brad

 

[butelja]

Why do European countries who try to badger the USA into metrification not fully follow their own advice. In the process industry, pressure is often referred to in km/cm^2, not in Pa, kPa, MPa, or bar? This is only one example of many I have run across.

 

[DaveVikingPE]

The metric rules seem to be lengths given in millimeters, area loads in kPa and volume in liters.

Wheee. I think we've all been using kilo-pounds for a long time, why change?

Now, I will gladly switch to metric when:

a) kilometer is pronounced correctly. It's a KILL-O-METER not a kilom-eter.

b) Length mesurement changes to Angstroms.

d) Volume is stricly given in deciliters.

 

[swertel]

I'll switch to metric when they finally get a decent thread pitch and tolerance for each thread size. Fine threads are too fine and course threads are too course.

And I still don't get the genious behind the tolerancing scheme. I put H7 on a drawing and the tolerance is different depending on the nominal hole size. What a PITA to remember. And why do I have to clarify between h7 and H7? Is capitalization that important on a drawing? What happened to being able to print everything in all caps for clarity. I'm surprised ISO/Metric drawing standards haven't allowed for cursive writing on the drawing face yet. SHEESH!

<end of rant... thanks for listening>

--Scott

 

[Haf]

Personally, I prefer to perform calculations using the SI system. While the system uses metric units, there is a standard metric unit for everything, and every standard unit reduces to kilograms, meters, and seconds. I try not to use prefixes on anything while doing calculations (ironicly, there is already a prefix on the kilogram standard, which always bothered me). There is less confusion that way, and I tend to make fewer mistakes. The main problem is that this system yields unwieldy numbers. So, in the end, I tend to convert the &quot;answer&quot; into &quot;convenient&quot; units. Usually, convenient is defined as a unit that allows for a &quot;pretty&quot; number.

For example, can you imagine an American bragging that their new Corvette had 260,995 Watts of power, instead of 350 horsepower? Or how about an American who bought a house on a 20,234 square meter lot, instead of a five acre lot? It's just not gonna happen! Each industry has units associated with it that usually allow the engineers to work with &quot;nice&quot; numbers, regardless of whether English or metric units comprise those units. Furthermore, those industries have used those units for so long that they have been ingrained into the culture. People begin to &quot;get a feel&quot; for those units. The major difference is that with metric units, there is a tendency towards using prefixes to tame numbers by factors of ten. In the English system, we show an utter disregard for the decimal system, invent a completely new unit, and usually try to give it a funny name.

America has already tried to switch to metric units. Simply put: it didn't take. Of course, at the time, people feared that switching to metric units was the first step towards switching to communism. Maybe now that the Cold War is over, we should give it another shot? My sneaking suspicion is that it still won't take.

Haf

 

[Hush]

Things could be worse.

Try living and working in Canada where we are caught in a eternal state of limbo between SI and Imperial. I listen to the morning news to find out the temperature in celsius while drinking a cup of coffee. Then I drive 15 kilometres to work at 30 miles per hour where I perform calculations on 7-1/16&quot; 35 MPa flange connections. On the way home I pick up a litre of milk and a pound of butter. I think you get the picture.

 

[RDK]

The world is metric. It’s just the US (and Yemen) that is not.

Because of our proximity to the US here in Canada we tend to use a hybrid system. Until our largest trading partner joins the remainder of the world in adopting the most rational system of measurement, we will continue to have vestiges of the imperial system.

To reject the metric system because no one wants to say that they bought a 20,234 sq m lot demonstrates that you simply do not understand measurement systems. Is the 5-acre lot exactly 5 acres to 5 significant digits? (5.0000) I think not. Why not buy a 2-hectare lot instead?

There are “nice” numbers in the metric system. My old Mopar 440 is now a 7.2-liter engine. Your Corvette puts out 261 kW. To have to remember a few prefixes (many of which we already use. How many Megs of RAM do you have in your computer, How many Gigahertz is the processor? How many kilobytes is that document file?) is a lot simpler than remembering that an acre has 43,560 sq ft or that there are 160 oz in a gallon (imperial not US gallon which is only 128 oz.) or that 60 MPH is 88 FPS. or any of a hundred different conversion factors necessary to work in the imperial system.

Yes, switching to the metric system is difficult. There are ingrained cultural reasons that make the conversion harder. Canada has been using Celsius for 28 years now and there are still some radio stations that give temperatures in Fahrenheit. We should have simply converted totally and not allowed soft conversions why not buy 500 g of butter instead of 454 g. Why are fluorescent light tubes 1 220 mm long? Why not 1 200 mm?
Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[Aton]

In this age of calculators, spreadsheets, programming, etc, in one sense it really shouldn't matter what system we use. Conversion utilities abound. And precision is simply a matter of what your needed tolerances are. Cabinetmakers work to 64ths of an inch, while machinists work to thousandths (or their metric equivalents). But: Hush is right on when he refers to our fractured lives here in Canada. I'm old enough to think and feel in Imperial, but must work professionally in metric. I still don't have any intuitive feel for a length of, say, 1500 mm (without first mentally translating to metres, and then on to yards each time), whereas the inch (still called &quot;un pouce&quot; - &quot;a thumb&quot; - in French), or the foot, are human-derived measures with which I am most connected. I can &quot;feel&quot; how much a pound weighs, but have trouble with much direct insight into kilonewtons. And then, of course: the concatenation of units with which we often deal (try deriving the fundamental units for specific enthalpy, or for dynamic viscosity) are complex enough, without worrying about conversions. Thank the exponents-that-be for computers!

RDK is right when he says that switching to metric is difficult. And I agree also that if we are going to switch, let's do it completely and never look back. It WOULD be far better to live and work in only one system - whatever it is! But this is not our reality here in the limbo of water that boils at two different integers.

The real trouble for us engineers, I think, springs from the danger of translation between the two systems, and the increased chance for error at that juncture. I do not know how others handle this situation, but I design structural systems in metric (because all our LSD-based codes are in metric), and at the very end where necessary, I convert to Imperial so that contractors and suppliers can understand what it is I am talking about.

As an aside: the study of units (and their historical beginnings) from a sociological perspective is fascinating in itself. Taking a purely intuitive approach, who of our not-so-distant ancestors would have ever dreamed that the fundamental units (&quot;fundamental&quot; in metric, that is) of mass, length, and time (two times, no less!), when combined in a certain way, would produce the unit of force? This is strange magic indeed. Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.

 

[Haf]

Well this certainly turned into an interesting discussion! Let me clear up some things.

As I mentioned, I prefer the metric system. I'm a recent grad, and most of the classes I took, both as an undergraduate and graduate student, exclusively used the metric system. Now that I'm working, however, I am almost forced into using the English system. Believe me, many of the engineers and scientists in the US would love to switch to the metric system (especially the younger ones), but, as RDK pointed out, it's tough to switch.

I must take exception with one of RDK's comments. Americans understand measurement systems just fine. In fact, one reason we can't seem to be able to kick the English system is because we have been trying to use measurement systems that are understandable. As Aton pointed out, the inch and the foot are human-derived measurements. Everyone has seen movies with carriages drawn by horses. We have a feel for the power of one horse, or six horses for a stage-coach. To this day, when I think of a Vette with 350 horse power, I think of 350 horses pulling that car! Unfortunately, the price we pay for using human-derived measurements is ugly conversion factors. Guess you can't have your cake and eat it too.

Engineers and scientists get used to using units they have no &quot;feel&quot; for. As Aton pointed out, almost no one has a feel for enthalpy or viscosity. Or how about entropy or thermal conductivity? Who has a feel for nanometers or picofarrads? Since engineers get used to working with these units, many have no qualms with switching to metric. As for the rest of the country, good luck!

Now for a little story. Not too long ago an unmanned NASA shuttle went off-course and was eventually lost in deep space. NASA engineers struggled to find the source of the problem, and recalculated their formulas and equations. It ended up that one systems group was using metric units and the other English. They had forgotten to convert into one language. And these guys were rocket scientists!

The unfortunate reality is that there will always be different measuring systems. Despite this, we can hopefully speak the same language in the end.

Haf

 

[butelja]

Here is a little light hearted story that explains many things.

The US standard railroad gauge (width between the two rails) is 4 feet, 8.5 inches. That's an exceedingly odd number. Why was that gauge used? Because that's the way they built them in England, and the US railroads were
Built by English expatriates. Why did the English build them like that? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge they used. Why did &quot;they&quot; use that gauge then? Because the people who built the tramways used
the same jigs and tools that they used for building wagons which used that wheel spacing.

Okay! Why did the wagons have that particular odd wheel spacing? Well, If they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England, because that's the spacing of the wheel ruts. So who built those old rutted roads?

The first long distance roads in Europe and England were built by Imperial Rome for their legions. The roads have been used ever since. And the ruts in the roads?

Roman war chariots first formed the initial ruts, which everyone else had to match for fear of destroying their wagon wheels. Since the chariots were made for (or by) Imperial Rome, they were all alike in the matter of wheel
spacing.

The United States standard railroad gauge of 4 feet, 8.5 inches derives the original specification for an Imperial Roman war chariot. Specifications and bureaucracies live forever!

So the next time you are handed a specification and wonder what horse's Ass came up with it, you might be exactly right, because the Imperial Roman war chariots were made just wide enough to accommodate the back ends of two war horses. Thus, we have the answer to the original question.

Now the extraterrestrial twist to the story...... When you see a Space Shuttle sitting on it's launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs. The SRBs are made by Thiokol at their factory in Utah.

The engineers who designed the SRBs might have preferred to make them a Bit fatter, but the SRBs had to be shipped by train from the factory to the launch site. The railroad line from the factory had to run through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is slightly wider than the railroad track, ..... and the railroad track is about as wide as two horses' behinds.

So, the major design feature of what is arguably the world's most advanced transportation system was determined over two thousand years ago by the width of a horse's ass.

And you wonder why it's so hard to make things change ...

 

[Hush]

butelja,

Thank you for an excellent (and elegant) summation of the issue.

 

[Aton]

Wonderful tale! Now, THAT'S the way history should be taught! butelja, you have made my day. Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.

 

[TheBlacksmith]

And I'm still confused. Many things are mis-named. The much used kilo-byte is actually 1024, not 1000. Computers are all digital - two states, on or off. The popular numbers used in computers are 256 - 2 to the eighth power, 512, 2 to the ninth power and 1024, 2 to the tenth power. Maybe we are supposed to have contradictory systems and numerous conversion factors. As pointed out, many Imperial measurements are based on observations - horse power, the approximate length of a human foot, the width of a horse's behind, whereas the metric system is based on base 10, which nobody learns until they go to school. Hmmm...

Blacksmith

 

[Aton]

You're right, Blacksmity: many different systems - and that's why we get the really big bucks, eh? Canadians can't talk about a 2x12 anymore. Instead, we are supposed to know that it is now officially a &quot;38x286&quot;.

But, at least within systems there is concerted movement toward standardization. In Medieval Europe, Ive read that each fiefdom (and sometimes each village within each fiefdom) had its own pole in the village square. On this pole was marked out yards, feet, and inches, etc), taken from the royal foot of a visiting local king at some time in the past. Each house-wright within the village district worked to the same measure, but woe betide a tradesman from another area - his measuring tools would be useless.

Of course, measures are not for everyone. Years ago, I hired an &quot;experienced&quot; carpenter to give me a hand framing. He was to read out lengths to me, and I was to cut to size. As I was waiting for the first length, I heard him mumbling to himself, and he finally called out, &quot;Eleven feet, four inches...and...seven of those tiny little lines.&quot; sigh.
Sustainable, Solar, Environmental, and Structural Engineering: Appropriate technologies for a planet in stress.

 

[vpl]

Sorry to burst a bubble here, but ... From &quot;TruthorFiction.com&quot; on the story of the width of railway tracks:

This story is a &quot;We've always done it that way&quot; tale. It says that the standard distance between railroad rails in the U.S. is four-feet, eight-and-a-half inches. Why? Because that's what it was in England. Why? Because that's the gauge the tramways used before the railroads. Why? Because the tramways were built using the same tools as wagon-builders and that's how wide the wagon wheels were spaced. Why? Because the old roads in England had ruts that the wheels needed to accommodate. Why? Because the ruts were made by Imperial Roman chariots.

The Truth: There is no evidence that we could find that this is true. In an article on

http://www.railway.org

by D. Gabe Gabriel says this tale has existed since shortly after World War II but that history does not support the claims of the story. The Roman ruts, according to Gabriel, were not for chariots but for narrow, hand-pulled carts. Although there are many places where the ruts are visible, Gabriel questions that they played a role in English railroad standards 1400 years after the last Roman legions. One of the claims of the eRumor is that the width of the ruts was affected by the need to make the chariot and it's wheels the same width as the combined rears of the horses pulling them. Gabriel says there's a statue by Franzoni in the Vatican museum that is regarded as the most accurate known depiction of a Roman chariot. The two horses are wider than the chariot and the chariot wheels behind them.

Where did the four-foot, eight-and-a-half-inch standard originate? Gabriel says it was from a Englishman named George Stephenson. Carts on rails had been used in mines in England for years, but the width of the rails varied from mine to mine since they didn't share tracks. Stephenson was the one who started experimenting with putting a steam engine on the carts so there would be propulsion to pull them along. He had worked with several mines with differing gauges and simply chose to make the rails for his project 4-foot, eight inches wide. He later decided that adding another six inches made things easier. He was later consulted for constructing some rails along a roadway and by the time broader plans for railroads in Great Britain were proposed, there were already 1200 miles of his rails so the &quot;Stephenson gauge&quot; became the standard.

Interestingly, the 4-foot, eight-and-a-half inch width has not always been the standard in the U.S. According to the Encyclopedia of American Business History and Biography, at the beginning of the Civil War, there were more than 20 different gauges ranging from 3 to 6 feet, although the 4-foot, eight-and-a-half inch was the most widely used. During the war, any supplies transported by rail had to be transferred by hand whenever a car on one gauge encountered track of another gauge and more than 4,000 miles of new track was laid during the war to standardize the process. Later, Congress decreed that the 4-foot, eight-and-a-half inch standard would be used for transcontinental railway.

updated 5/30/02

Patricia Lougheed

 

[butelja]

Technically superior to my answer, but not nearly as entertaining.

 

[Hush]

Call me gullible but I'm still not going to completely discount bujela's tale until someone actually finds some old cart ruts and measures them, if for no other reason than it makes me smile. Besides, for all we know Stephenson measured some ruts on his way to work that morning. I also seem to remember something about the Romans (or was it the Chinese) setting a standard wheelbase for the empire to ensure their armies could move easier (of course my brain has been known to occasionally create a 'fact' to support a pet theory).